Constrained folded path resonant white light scintillator

ABSTRACT

An optical emitter enabling conversion of light from a light source. The optical emitter includes a first conic reflector defining an aperture for receiving the light source, a second conic reflector opposite the first conic reflector for collimating light emitted by the light source, and a volumetric light conversion element between at least a portion of the first reflector and at least a portion of the second reflector. The optical emitter can also include a convex mirror adjacent the vertex of the second conic reflector, and an elliptical element adjacent the first conic reflector. The light conversion element can include phosphor dispersed in a resin to convert light from a first wavelength to light of a second, longer, wavelength, wherein converted light is emitted from the light conversion element.

FIELD OF THE INVENTION

This invention relates to light sources and the manufacturing of lightsources. In particular, this invention relates to light sources and“light engines” that are used for specific light tasks including, forexample, flash lights, automotive lights, streets and public areas aswell as industrial area lighting and medical illumination.

BACKGROUND OF THE INVENTION

With the development of the Light Emitting Diode (LED) for use in thelighting industry, the opportunity for energy savings continues to besignificant for individuals and society as a whole. A major hurdleimpeding the realization of energy savings, however, is the cost ofinstallation or manufacturing. In particular, many of the newtechnological improvements which greatly improve the luminous efficacyof white LEDs come with disadvantages in the manufacturing process.

In the manufacturing of a common white light LED, a phosphor powderblend is normally mixed with an encapsulant and deposited as a layeronto the surface of an emitter junction. Many emitter junctions arenarrow wavelength band blue or near ultraviolet (UV) diodes, with a FullWidth at Half Maximum (FWHM) of only 40 nm. The phosphor blend iscreated to absorb the blue or UV wavelengths and reemit broadband greento red wavelengths. The ratio of blue absorption to secondary green tored emissions determines the color temperature of the emitted whitelight. This is a straightforward process and as such any improvements toincrease the luminosity output add complications to this process whichcan increase the manufacturing cost.

Failures that plague the above approach include heat degradation of thephosphor due to its proximity to the emitter junctions. The emitterjunctions run at relatively high temperatures (>70 deg C.) against anambient background (25 deg C.). The encapsulant degrades with highertemperatures, often resulting in discoloration and inefficienttransmitters in the blue or the visible wavelength region. Additionally,the encapsulant acts as a thermal blanket on top of the emitterjunctions causing a further loss of efficiency. Close proximity of thephosphor layer to the emitter junctions also creates an additional lossof white luminosity, as efficient emitters by definition (thermo-dynamicblackbodies) must also be efficient absorbers, thus white lightgenerated near the emitters is lost energy.

There exists another limitation to the above approach: the relativelysmall area of emission. This creates an increase in luminosity butspreads the light output over a small cone angle, thus creating a veryhigh brightness. Such brightness levels can pose a threat to the humanvision system and can contribute to migraines, seizures, and temporarywashout of the human eye. Yet another limitation to the above approachis that it is not directly scalable. It is not an easy task to increaseluminosity by adding more emitter junctions and thicker layers ofphosphor. Such endeavors increase the heat load in a non-linear waywhile adding more of the “blanket” effect from the phosphor encapsulant.

SUMMARY OF THE INVENTION

The aforementioned problems are overcome by the present invention whichincludes a volumetric light emitter that can be manufacturedindependently of an emitter junction. The volumetric light emitterincludes a first conic reflector including an aperture for a lightsource or an emitter junction, a second conic reflector opposite thefirst conic reflector for collimating light emitted by the light source,and a volumetric light conversion element extending between at least aportion of the first reflector and at least a portion of the secondreflector.

In one aspect of the invention, the light conversion element includesphosphor particles dispersed in a resin to convert light emitted by thelight source from a first wavelength to a second wavelength, the secondwavelength being longer than the first wavelength. As disclosed, thelight conversion element is substantially solid, and includes an annularouter surface, wherein light is emitted through the annular outersurface in a generally toroidal pattern. Additionally, the lightconversion element preferably includes a cylindrical portion or afrusto-conical portion being coaxial with the first and second conicreflectors.

In another aspect of the invention, the first conic reflector iselliptical and the second conic reflector is parabolic. The volumetriclight emitter includes a negative minor adjacent the vertex of thesecond conic reflector. Additionally, the volumetric light emitterincludes an elliptical element adjacent the first conic reflector,wherein the first conic reflector and the elliptical element define acoextensive aperture for the light source.

The volumetric light emitter can be optically bonded to one or moreemitter junctions as a final step, thus creating a simple volumetriclight engine wherever a light filament or arc may be used. Thisinvention acts as a bridging technology between LED junctionmanufacturers and luminaire manufacturers, which delivers the lightingrequirements to the end user. This allows for a common design to beimplemented with a variety of LED junctions and heat sink arrangements.Another benefit of this invention lies in integrating three specificoptical tasks into one simple and manufacturable form. The three opticaltasks are: 1) light gathering and placement from emitter junctions, 2)improving utilization and containment of pump light, and 3) downconversion and emission of white light. This integration opens up newdesigns for luminaires and possesses the benefit of ease of retrofittingolder structures with LED sources.

These and other advantages and features of the invention will be morefully understood and appreciated by reference to the drawings and thedescription of the current embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a first embodiment of the invention.

FIG. 2 is a cross-sectional view of the volumetric light emitter in FIG.1.

FIG. 3 is an optical ray trace of a cross-sectional view of a variationof the volumetric light emitter in FIG. 1.

FIG. 4 is an optical ray trace of a cross-sectional view of a variationof the volumetric light emitter in FIG. 1.

FIG. 5 is an optical ray trace of a cross-sectional view of thevolumetric light emitter in FIG. 1.

FIG. 6 is an optical ray trace of a cross-sectional view of thevolumetric light emitter in FIG. 1 illustrating a ray trace impinging aconvex mirror.

FIG. 7 is an optical ray trace of the volumetric light emitter in FIG. 1illustrating a ray trace impinging the outer annular surface of thelight conversion element.

FIG. 8 is an optical ray trace of a cross-sectional view of a variationof the volumetric light emitter in FIG. 1.

FIG. 9 is an optical ray trace of a cross-sectional view of a secondembodiment of the present invention.

FIG. 10 is an optical ray trace of a cross-sectional view of a thirdembodiment of the present invention.

FIG. 11 is an optical ray trace of a cross-sectional view of a fourthembodiment of the present invention.

FIG. 12 is a graph illustrating the output spectral distribution of aphosphor light conversion element within a Constrained Folded PathCavity in accordance with an embodiment of the present invention.

DESCRIPTION OF THE CURRENT EMBODIMENT

A main focus of conventional LED research is to maximize luminositywhile reducing the energy consumption, i.e., luminous efficacy. Eventhough this seems to be the best path to success, it is fraught withgains in luminosity which are not practical for the mass productionenvironment that white LED-based luminaries will need to be at. A wiserapproach is to look at the costs of producing white luminosity. Thesecosts break down to operational costs and implementation costs. It isthe great savings in operational costs to our society that is drivingthe development of this technology. However it is the implementationcost that becomes the biggest barrier to moving forward. The presentinvention addresses this cost barrier—the implementation cost barrier.This is the problem we as a society are trying to solve; themaximization of white luminosity while reducing the number ofmanufacturing steps involved in reaching the end use luminaire. Asexplained herein, the present invention can perform three distinctoptical functions in a single molded component. The first optical taskis to gather the light from the LED junction source and convert it to amore usable format. The second optical task is to create a gain functionin the intensity of the Deep Blue Light (DBL) while constraining the DBLlosses. The third optical task is to create an optical environment forbest down conversion efficiency. As explained below, the three opticalfunctions lead to improvements on seven parameters which cause theluminosity to produce high performance and which offer a simplemanufacturable design. Due to its single piece layout, the presentinvention also lends itself to cost effective manufacturing.

With the above optical tasks in mind, the present invention provides avolumetric light emitter which constrains DBL into a light conversionchamber to thereby control losses and maximize the probability of whitelight generation via phosphorescence. This is achieved, in part, bymaking use of a concept from laser physics: the resonant cavity. Thepurpose of a resonant cavity is to confine the DBL such that the onlyloss in the DBL is from the excitation of the phosphors within theresonator structure. The Applicant acknowledges that the requirements ofan operational laser resonant cavity—High Q status, cavitylength=N×Wavelength, Spectral Line width of 1 nm, etc—cannot be achievedfrom an LED source. The terms ‘resonant cavity’ and ‘resonant structure’are used as a descriptor in creating a visual reference for describingthe present invention. This resonant structure, or Constrained FoldedPath Cavity (CFPC), possesses reflectors at opposite ends. One purposeof the CFPC is to cause the DBL to repeat its path of propagation anumber of times over, while reducing the number of exit paths that allowthe DBL to escape. Current repeat propagations vary between 4 and 40,depending on the resonant model chosen, not in the thousands or millionsas required for a laser resonant cavity. This will increase theintensity of DBL while keeping it contained within a known volume. Oneembodiment of the resonant structure is the hemi-confocal cavitystructure as shown in FIGS. 1-8, though the invention may utilize otherforms of multi-pass folded structures.

In addition to constraining DBL in a resonant cavity, the volumetriclight emitter radiates Down-Converted White Light (DCWL) in a toroidalor a spherical pattern. This is accomplished by using a remote phosphorblended into a resin material, which forms a three-dimensional orvolumetric light conversion element in the resonant structure of theCFPC, thus creating a volumetric white light radiator In the presentembodiment, a phosphor, such as EY4453 by Intematix, is premixed into anacrylic, polycarbonate, Nylon, or polystyrene resin for injectionmolding, such as Nylon 6/66 by BASF (marketed as ULTRAMID®). Thephosphor-doped light conversion element can optionally be molded withthe curvatures of the reflectors of the CFPC. Additionally, the densityof the phosphor is such that the volumetric light conversion element istranslucent to the DBL, not opaque. For example, if the DBL will make 6reflections within the CFPC, then it is desirable to absorb 16.67% perpass with total absorption at 100% for 6 reflections. It is alsopossible to utilize this technology with castings, extruding, pressforms, or machining to achieve the desired form.

The volumetric white light emitter of the present invention may also beused in conjunction with an optical coupler, such as the optical couplerdisclosed in U.S. patent application Ser. No. 12/405,398 to Bourget,filed on Mar. 17, 2009, and titled “High Efficiency Optical Coupler,”which is incorporated herein by reference. In particular, a HighEfficiency Optical Coupler (HEOC) can convert a Lambertian source into anon-Lambertian radiator to reduce the Numerical Aperture (N.A.) of thesource light. This improves the “usability” of the DBL. By choosing thecorrect radii and conics, a bi-modal intensity pattern output can becreated, and the HEOC can to collect up to 98% of all DBL and place itwhere it is most likely that blue photons will interact with phosphormaterials. Accordingly, the present invention combines a HEOC, aconstrained folded path cavity, and a toroidal radiator into a singleelement. Several benefits can accrue from the present invention:

(1) more efficient transfer (up to 98%) of DBL into the phosphorescenceregion;

(2) “resonant” coupling within the phosphorescence region for multi-passintensity gain of DBL;

(3) reduced white light loss due to reabsorption at the emissionjunction(s);

(4) less complex heat sink and heat sink costs due to heat flowimprovement attributed to the flexibility of location of the emitterjunction(s);

(5) improved temperature stability and less temperature light outputdegradation due to remote phosphor effect;

(6) fine tuning of chromaticity based on cavity length; and

(7) reduced manufacturing loss yields due to fewer mechanical operationsat the emitter junction(s).

Accordingly, the embodiments of present invention provide multipleimprovements.

I. First Embodiment

A volumetric white light emitter in accordance with an embodiment of thepresent invention is illustrated in FIGS. 1-8 and generally designated20. The volumetric white light emitter 20 includes a first conicreflector 22, a second conic reflector 24, and a volumetric lightconversion element 26 extending between the first conic reflector 22 andthe second conic reflector 24. The first conic reflector 22 defines anaperture 28 for a light source or emitter junction (not shown), and thesecond conic reflector 24 is orientated opposite the first conicreflector for reflecting light from the light source toward the firstreflector 22. A convex minor 32 is positioned adjacent the vertex 34 ofthe second conic reflector 24. The second conic reflector 24 is shown asparabolic with a focus at the aperture 28 of the first conic reflector22. Additionally, an elliptical element 38 is positioned adjacent thefirst conic reflector 22. The elliptical element 38 defines an aperture40 coincident with the first reflector aperture 28 to direct light fromthe light source toward the second conic reflector 24. The volumetriclight conversion element 26 includes phosphor particles dispersed in ahardened resin to convert light emitted by the light source from a firstwavelength to a second wavelength, the second wavelength being longerthan the first wavelength. The volumetric light conversion element 26also includes an outer annular surface 30 to radiate converted light ina generally toroidal pattern. As also shown in FIGS. 1-2, the volumetriclight conversion element 26 is generally frusto-conical or cylindrical,and is coaxial with the first and second conic reflectors 22, 24.

As explained below, the volumetric white light emitter 20 can be adaptedto accommodate a specific LED based on its peak emission wavelength. Forexample, the volumetric white light emitter 20 of the present embodimentis configured to down-convert DBL light from an LED junction having aDBL emission wavelength of 455 nm. The volumetric light conversionelement 26 includes a phosphor chosen with a main radiation peak of 570nm (Yellow) and a FWHM of 90 nm—a typical “off the shelf” phosphormaterial. The design goal is to convert at least 80% of the emitted bluelight into the yellow light output. The blending of the remaining bluelight and the phosphorescent yellow light creates to the human eye alower Color Rendering Index (CRI) of white light (while lower CRI lightis not accurate for color measurement, it is adequate for many generalillumination applications). For a single junction system with anemission area of 1.3 mm sq. having 1.14 mm on a side, typicaloperational parameters include an operating current (lop) of 350 mAmpswith a voltage drop of 3.4 Vdc for a power consumption of 1.2 Watts. Atypical output conversion efficiency of 25% yields a radiant power of0.3 Watts. Expressed as luminosity, the value at 455 nm with 36.5lm/Watt×0.3 Watts equals 11 lumens of blue light.

The second conic reflector 24 is selected to have a diameter about tentimes larger than the baseline of the emitter. In the presentembodiment, this sets the operational diameter of the second conicreflector 24 at 11. mm. For a surface mount junction, the angle for theFWHM of the Lambertian intensity distribution is typically 60 degrees,corresponding to an N.A. of 0.866. For light propagating through anacrylic resin medium (Index of Refraction=1.497), this same N.A. createsthe angle of intensity of 35.4 degrees. This angle is used incombination with the operational diameter to calculate the radius of thesecond reflector 24 and the cavity length. As noted above, one purposeof the second conic reflector 24 is to collimate the reflected rays anddirect them toward the first conic reflector 22. From the Minor Formula,a mirror's radius being equal to twice the focal length, sets the radiusof the second conic reflector 24 equal to the twice the length from theemitter junctions to the second conic reflector 24:

Radius of Second Reflector=2×(11.4 mm/2)/Tan 35.4°=16.0 mm.

This suggests that the cavity volume be roughly 0.82 cm³ from thefollowing formula:

V=Pi×R ² ×L

While the second conic reflector 24 is parabolic with a numerical conicvalue of −1.00, it is also possible to make variations in the conic,thus changing the shape from hyperbolic to spherical based on thedesired cavity constraints.

The purpose of the first conic reflector 22 is to gather the collimatedlight from the second conic reflector 24 and bring it to a focal plane.It is desirable, however, to set the focal plane to intersect a point onthe second conic reflector 24 such that the ray path of the DBL crossesthe main Z axis 42 and retraces its path back to the emitter junctions.The choice here is how many reflective paths to have between the firstand second conic reflectors 22, 24. In the current embodiment we have 6reflections as illustrated in FIG. 3, however some models havedemonstrated up to 40 reflections as illustrated in FIG. 4. The numberof reflective paths is based on the phosphor density appropriate tocreate the down converted white light. More reflective paths will meanmore DBL will be absorbed for a given density of phosphor. This impliesa warmer 3000 k type of light will be generated. In the currentembodiment, the first conic reflector 22 is an ellipse with a conicvalue of −0.8., though a range from −0.7 to −0.9 is appropriatedepending on the design of resonator. As mentioned above with the secondconic reflector 24, the first conic reflector 22 may take any conic formwhere the refocus conditions allow a retrace over previous paths Asshown in FIG. 5, a small positive element, for example an ellipticalminor 38, is placed at the vertex of the first conic reflector 22. Theelliptical mirror 38 gathers DBL that is emitted at or near 90° to thesurface of the emitter junctions. Another benefit is the reduction ofthe coupler outside diameter which can be achieved by breaking the firstconic reflector 22 into two discontinuous elliptical curves. The conicconstant of the first conic reflector 22 is maintained while the radiusof curvature and the diameter are significantly reduced. The curves canbe produced as separate components or as a single molded or machinedelement.

It is preferable to add a small negative element, for example a convexminor 32, placed at or adjacent the vertex 34 of the second conicreflector 24 to diverge the near axial propagated light emitted from theemitter junction(s). Without this negative element 32, reflected DBL offof the second conic reflector 24 can retrace its path along the mainaxis 42 and intersect the junction(s) surface. The diameter of thenegative element 32 will normally not be greater than one-third of thediameter of the second conic reflector 24. As shown in FIG. 6, thevertex 44 of the negative element 32 is located before the vertex 34 ofthe second conic reflector 34 along the main Z axis 42. The radius ofthe negative element is chosen so as to transfer the reflected rays tothe outside of the first conic reflector 22. As shown in FIG. 7, therays will normally reflect off of the first conic reflector 22 andintersect the outside wall 30 of the resonant cavity 20 with a shallowangle of incidence to have substantial internal reflection, assisting inkeeping the DBL confined within the cavity structure. After theplacement of the negative surface a refocusing of the first conicreflector 22 may be required. The focal point of the first conicreflector 22 can be on the surface of the negative element 32 tofacilitate the retracing of the optical path.

The luminous output spectral distribution of the volumetric white lightgenerator of FIGS. 1-8 is illustrated in FIG. 12. The solid linerepresents the luminous output from a known phosphor, and the brokenline represents the same phosphor operating within a constrained foldedpath cavity. The difference in the output illustrates increased lumensproduced by the cavity structure in accordance with the presentembodiment. Though shown above in connection with an LED having a DBLemission wavelength of 455 nm, the volumetric toroidal radiator 20 canalso be adapted to accommodate an LED with an emission wavelength of 405nm, for example. The phosphor blend may have a broadband radiation peakfrom 480 nm (cyan) to 630 nm (red) and a FWHM 200 nm—a custom blendedphosphor material. Again, the goal is to convert up to 100% of theemitted blue light into a broadband white light output by constrainingthe DBL in the volumetric white light radiator 20 and down-convertingDBL light via the phosphorescent element 26. This brings forth aphosphorescent white light which to the human eye has a higher CRIrating. To accommodate the DBL wavelength of 405 nm, the length of thevolumetric toroidal radiator 20 is increased to allow more absorption ofthe DBL on a per reflection basis as shown in FIG. 8. This is incombination with more reflections, for example 8 or 10, within theresonant cavity. This will dictate a longer radius on the first andsecond reflectors 22, 24 as well as on the negative element 32. Theconic constant of the first conic reflector 22 may also increase todrive the ellipse to act more as a parabolic form.

II. Second Embodiment

A folded spherical cavity 50 in accordance with another embodiment ofthe present invention is shown in FIG. 9. The folded spherical cavity 50includes a spherical reflector 52, a planar reflector 54 opposite thespherical reflector 52, and a volumetric light conversion element 56extending between the spherical reflector 52 and the planar reflector54. The spherical reflector 52 defines an aperture or seat (not shown)for a light source or emitter junction. Though not shown, a convex minorcan be positioned adjacent the planar reflector 54. Additionally, anelliptical element (not shown) can be positioned adjacent the sphericalreflector 52. The elliptical element can also include an aperturecoincident with the spherical reflector aperture to direct light fromthe light source toward the planar reflector 54. The volumetric lightconversion element 56 includes phosphor particles dispersed in a resinto convert light emitted by the light source from a first wavelength toa second wavelength, the second wavelength being longer than the firstwavelength. The volumetric light conversion element 56 also includes anouter annular surface 60 to radiate converted light in a generallytoroidal pattern. As also shown in FIG. 9, the volumetric lightconversion element 56 includes a generally frusto-conical portion 58proximate the planar reflector 54 and coaxial with the sphericalreflector 52.

III. Third Embodiment

A folded transverse cavity 70 in accordance with an embodiment of thepresent invention is shown in FIG. 10. The folded transverse cavity 70includes a frusto-conical reflector 72, a conic reflector 74 oppositethe frusto-conical reflector 72, and a volumetric light conversionelement 76 extending between at least a portion of the frusto-conicalreflector 72 and at least a portion of the conic reflector 74. Thefrusto-conical reflector 72 defines an aperture or seat (not shown) fora light source or emitter junction (not shown). The conic reflector 74is orientated opposite the frusto-conical reflector 72 for reflectinglight from the light source toward the frusto-conical reflector 72. Aconvex minor 78 is positioned adjacent the vertex 80 of the conicreflector 74. The conic reflector 74 is shown as parabolic with a focusat the aperture of the frusto-conical reflector 72. Though not shown, anelliptical element can be positioned adjacent the frusto-conicalreflector 72, including an aperture coincident with the first reflectoraperture to direct light from the light source toward the conicreflector 74. The volumetric light conversion element 76 includesphosphor particles dispersed in a resin to convert light emitted by thelight source from a first wavelength to a second wavelength, the secondwavelength being longer than the first wavelength. The volumetric lightconversion element 76 also includes an outer annular surface 82,radiating converted light through the outer annular surface 82 in agenerally toroidal pattern. As also shown in FIG. 10, the volumetriclight conversion element 76 is generally cylindrical and coaxial withthe conic reflector 74.

IV. Fourth Embodiment

A folded confocal cavity 90 in accordance with an embodiment of thepresent invention is shown in FIG. 11. The folded confocal cavity 90includes a planar reflector 92, a conic reflector 94 opposite the planarreflector 92, and a volumetric light conversion element 96 extendingbetween at least a portion of the planar reflector 92 and a portion ofthe conic reflector 94. The planar reflector 92 defines an aperture orseat (not shown) for a light source or emitter junction (not shown). Theconic reflector 94 is orientated opposite the planar reflector 92 forreflecting light from the light source toward the planar reflector 92. Aconvex minor 98 is positioned adjacent the vertex 100 of the conicreflector 94. The conic reflector 94 is shown as parabolic with a focusat the aperture of the planar reflector 92. Though not shown, anelliptical element can be positioned adjacent the planar reflector 92,including an aperture coincident with the planar reflector aperture todirect light from the light source toward the conic reflector 94. Thevolumetric light conversion element 96 includes phosphor particlesdispersed in a hardened resin to convert light emitted by the lightsource from a first wavelength to a second wavelength, the secondwavelength being longer than the first wavelength. The volumetric lightconversion element 96 also includes an outer annular surface 102,radiating converted light through the outer annular surface 102 in agenerally toroidal pattern. As also shown in FIG. 11, the volumetriclight conversion element 96 is generally cylindrical and coaxial withthe conic reflector 94.

V. Conclusion

The above embodiments include a volumetric light emitter that can bemanufactured independently of the emitter junction or other lightsource. The volumetric light emitter can be optically bonded to theemitter junctions or other light source as a final step, thus creating asimple volumetric light engine to radiate down-converted white light ina toroidal, spherical, or other pattern.

The above descriptions are those of current embodiments of theinvention. Various alterations and changes can be made without departingfrom the spirit and broader aspects of the invention as set forth in thefollowing claims, which are to be interpreted in accordance with theprinciples of patent law including the Doctrine of Equivalents.

1. An optical emitter comprising: a first conic reflector including afirst reflector vertex and adapted to receive a light source proximatethe first reflector vertex; a second conic reflector coaxial with thefirst reflector, the first and second conic reflectors facing oneanother to define a folded path cavity therebetween; and a volumetriclight conversion element between at least a portion of the first conicreflector and at least a portion of the second conic reflector withinthe folded path cavity, wherein the volumetric light conversion elementis adapted to down-convert light reflected between the first and secondconic reflectors and emit the down-converted light generally radiallyoutward from between the first and second conic reflectors.
 2. Theoptical emitter of claim 1 wherein the first conic reflector defines anaperture at the first reflector vertex.
 3. The optical emitter of claim1 wherein the volumetric light conversion element interconnects thefirst and second conic reflectors.
 4. The optical emitter of claim 1wherein the light conversion element includes a plurality ofwavelength-converting phosphors.
 5. The optical emitter of claim 1wherein the light conversion element includes an annular outer surfaceto form at least one of a cylindrical exterior and a frusto-conicalexterior.
 6. The optical emitter of claim 1 wherein the first conicreflector is elliptical.
 7. The optical emitter of claim 1 wherein thesecond conic reflector is parabolic.
 8. The optical emitter of claim 1wherein the first conic reflector vertex is located at the focus of thesecond conic reflector.
 9. The optical emitter of claim 1 furthercomprising a convex mirror adjacent the second conic reflector andcoaxial with the first conic reflector.
 10. The optical emitter of claim1 further comprising an elliptical element coaxial with the first conicreflector, wherein the first reflector vertex is aligned with one of theelliptical element focus and the elliptical element vertex.
 11. A lightemitter comprising: a first reflector defining an aperture for a lightsource; a second reflector opposite the first reflector, at least one ofthe first and second reflectors being a conic, the first and secondreflectors defining a folded path cavity therebetween; and a volumetriclight conversion medium within the folded path cavity, the volumetriclight conversion medium including phosphor dispersed in a resin toconvert light emitted by the light source from a first wavelength to asecond wavelength, the second wavelength being longer than the firstwavelength, wherein the volumetric light conversion medium radiateslight at the second wavelength generally radially outward from betweenthe first and second reflectors.
 12. The light emitter of claim 11wherein the light conversion medium is substantially solid.
 13. Thelight emitter of claim 11 wherein: the light conversion medium includesan annular outer surface; and the converted light is emitted through theannular outer surface in a generally toroidal pattern.
 14. The lightemitter of claim 11 wherein the first reflector is a discontinuous conicreflector.
 15. The light emitter of claim 11 wherein the lightconversion medium is injection molded.
 16. An optical emittercomprising: a first conic reflector; a second conic reflector oppositethe first conic reflector; a third conic reflector opposite the secondconic reflector and adjacent the first conic reflector; a negative minoradjacent the vertex of the second conic reflector; and a translucentlight conversion element between the first and second conic reflectors,wherein the translucent light conversion element emits light generallyradially outward from between the first and second reflectors.
 17. Theoptical emitter of claim 16 wherein the first and third conic reflectorsdefine a coextensive aperture for a light source.
 18. The opticalemitter of claim 16 wherein the first, second and third conic reflectorsare coaxial.
 19. The optical emitter of claim 16 wherein the lightconversion element extends between at least a portion of the first conicreflector and at least a portion of the second conic reflector.
 20. Theoptical emitter of claim 16 wherein the light conversion elementincludes phosphor dispersed in a resin to convert light emitted by thelight source from a first wavelength to a second wavelength, the secondwavelength being longer than the first wavelength.